The Dapsone/creatinine ratio in random samples of urine was determined in 910 infectious leprosy patients attending the outpatient department of the Acworth Leprosy Hospital, Bombay during the period 20-9-76 to 20-11-1976. It was found that 48.7% of them were not taking regular treatment. The patients who were detected to be irregular in treatment were interviewed when they next attended the clinic to find the reason behind their irregularity. It was noticed that the majority of them (63%) attended the clinic for DDS treatment but could not come regularly for valid reasons, e.g. no time to attend, no money to travel to the clinic and absence from Bombay to go to native village.